Bakersfield Night Sky - December 16, 2018
by Nick Strobel
The William M Thomas Planetarium is closed during Bakersfield College's winter break. Evening public shows start back up in mid-February.
At the beginning of this month, NASA’s OSIRIS-REx arrived at the Near-Earth Asteroid Bennu. Since then, OSIRIS-REx (“Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer”) spacecraft has been flying alongside Bennu about 12 miles from the asteroid’s sun-facing side, executing a set of flyovers of Bennu’s poles and equatorial region that get it to within 4 miles during each flyover. At the end of the month, OSIRIS-REx will go into orbit around Bennu at a distance of just 0.75 miles. The name “Bennu" (after a mythical Egyptian bird) was chosen by a naming contest because the catalog name “1999 RQ36” is a bit a mouthful.
Bennu looks like a rubble pile glob shaped roughly like a diamond about 1600 feet across. Bennu is a primitive B-type asteroid rich in carbon and organic molecules which makes it interesting for astrobiology purposes. It is also interesting because Bennu comes very close to Earth every six years and there is a 0.037% chance that it will hit Earth in the late 22nd century (the year 2175 to be more precise). OSIRIS-REx will test out the “gravity-tractor” method of changing Bennu’s path using the weak gravity pull from the spacecraft. Like investing small amounts of money continuously over a long time can build up a large nest egg, the gravity-tractor method can work if the asteroid is discovered far enough in advance of collision with Earth to give the spacecraft’s gravity enough time to slightly change the asteroid’s orbit. The greater the allowed time to act, the smaller the change in the asteroid’s orbit needs to be.
OSIRIS-REx will do very high-resolution mapping and spectroscopy of Bennu’s surface and its gravity field to determine Bennu’s interior structure as well as finding the best spot to extract a sample to return to Earth. This intense scrutiny of Bennu before collecting a sample will take about a year and half. In July 2020 OSIRIS-REx will make up to three attempts to collect between 60 grams and 2 kilograms of Bennu material. Further study of Bennu will follow until the window for departing Bennu opens in March 2021.
In September 2023, OSIRIS-REx will reach earth and eject the Sample Return Capsule that will land in the same military test range in Utah used by the Stardust mission in January 2006. OSIRIS-REx’s capsule and re-entry equipment is the same as that used by Stardust. It will take another two years to analyze the Bennu sample. At least 75% of the sample will be stored at Johnson Space Flight Center for other science teams, including future generations of scientists, to study. Go to www.asteroidmission.org to learn more about the mission.
Much farther out in the solar system, the New Horizons spacecraft that flew by Pluto in July 2015 is going to fly by the Kuiper Belt Object 2014 MU69, nicknamed “Ultima Thule”, on New Year’s Eve Pacific Time. The closest approach will be just 2200 miles at 9:33 p.m. Pacific Time. We’ll have to wait a little over six hours for the radio signals beamed from New Horizons to reach us on Earth. It’ll take another day of processing the initial data set, so we don’t expect any pictures to be released until January 2.
For the past three weeks New Horizons has been looking for signs of small moons, rings, and dust around Ultima and the decision will be made today (December 16) on whether to stick with the close approach as originally planned or to divert the spacecraft to a safer distance for the flyby. Ultima is just 16 to 19 miles across but that’s about ten times larger than the typical comet that comes from the Kuiper Belt. New Horizons will fly by Ultima at 14.4 km/sec (over 32,000 mph), so it has just a few hours to make all of its observations.
At Ultima’s great distance the data transmission rate is only about 1000 bits per second and the New Horizons team has to share time with other space missions on the the Deep Space Network’s communication antennae. Therefore, it will take about 20 months to get all of the data beamed back to us from the flyby. One thing you learn in space missions is patience!
Speaking of patience, the LIGO and Virgo teams announced another four gravitational wave events from the merger of black holes. One event took place 5 billion years ago when two black holes of mass 34 and 51 solar masses spiraled inward and merged to form an 80-solar mass beast. Five solar masses were converted into the energy of the gravitational waves that travel at the speed of light. As of now the tally of black hole mergers that have been detected is ten and one neutron star-neutron star merger has been observed. The observing runs ended in 2017 and will resume in late March 2019 with even more sensitive detectors. Undoubtedly, a lot more mergers are going to be observed!
One last note: the December solstice that marks the beginning of our winter will happen on December 21. The sun will stop its southward drift among the stars at 2:23 p.m. Pacific Time. Enjoy the longest night of the year and I wish you many blessings this holiday season and a great 2019!